JPH11224459A - Video signal processing device - Google Patents

Abstract

(57) Abstract: Provided is a video signal processing apparatus having an FM demodulator at low cost and with little performance degradation by interpolating data of a digital reproduction FM luminance signal by an interpolation filter. A tan-type FM demodulator for digitally encoding an input FM signal and performing FM demodulation with a signal having a phase difference of 90 degrees with respect to the digital FM signal at all times to reduce a noise level at the time of demodulation. A video signal processing device comprising a bit precision extension means for improving data precision and increasing a bit width in an input section of the FM demodulator.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to digitization of video signal processing of a VTR, and more particularly to a video signal processing apparatus having an inexpensive and highly accurate FM demodulator.

[0002]

2. Description of the Related Art As is well known, a home VTR separates an input composite video signal into a luminance signal and a chrominance signal, and then converts the luminance signal into an FM modulation signal and the chrominance signal into a low-frequency conversion chrominance signal. Each of them is frequency-multiplexed and recorded on a magnetic tape.

Conventionally, as means for digitizing a reproduced FM luminance signal of the VTR and demodulating it into a reproduced video signal,
There are the following. A / A
The reproduced FM luminance signal quantized by the D converter is input to a 90-degree phase delay filter that always has a phase difference of 90 degrees with respect to the input signal. As a result of dividing the signal (hereinafter referred to as a cos signal) whose phase is delayed by 90 degrees from the reproduced FM luminance signal by the 90-degree phase delay filter and the reproduced FM luminance signal, a tangent (hereinafter referred to as tan) component of the reproduced FM luminance signal is obtained. Is extracted. A method of calculating an angular frequency from an output of a memory for calculating an arc tangent with respect to the input address and calculating a phase component and using the tan component as an input address and setting a deviation is introduced as a tan-type FM demodulator (ITE). Technical Report vo
l.18, No.72, PP.119-124, CE'94-43 (Nov.1994)).

[0004]

As described above, tan
Since the type FM demodulator obtains an angular frequency from the instantaneous phase difference between the reproduced FM luminance signal input to the FM demodulator and the cos component, and calculates the demodulation output from the angular frequency, the demodulation accuracy is equal to the input. Depends on the phase component of the signal. Therefore, in order to reduce the noise component at the time of demodulation and secure an accurate demodulated output, it is necessary to quantize the analog reproduced FM luminance signal as finely as possible. It has been confirmed by the inventor's verification experiment that the output requires at least a digital output of 9 bits or more.

However, in a high-band recording VTR, 5M
Recording and reproduction are performed up to a signal of about hz. Further, since the carrier frequency of the Hi8 standard VTR is 5.7 Mhz to 7.7 Mhz, the necessary band is about 0 to 13 Mhz in consideration of the above 5 Mhz band. In order to accurately restore the reproduced FM luminance signal, it is necessary to secure at least a band up to a side band of the FM signal during the processing of the FM signal band of the FM demodulator.

Also, taking into account the sampling theorem that can handle data of only half the frequency of the system clock with the digitization of signal processing, the system clock of the FM demodulator is at least 26 Mhz or more, and about 28 Mhz in consideration of the margin. Must be set. Accordingly, the A / D converter also has a system clock of 28 Mh.
A device that can operate at a high speed of z or more must be used.

Therefore, the A / D converter is required to operate at a high speed of 9 bits or more and 28 Mhz or more.
However, the market price of the A / D converter IC that satisfies the above conditions is expensive at present, and leads to an increase in the price of the digital LSI. Therefore, A / D with high speed and large number of bits
The use of a converter hinders system cost reduction.

An object of the present invention is to solve the above problem by using an inexpensive A / D converter having a relatively small number of bits which can be built in, and interpolating the output of the A / D converter using an interpolation filter,
It is an object of the present invention to provide a video signal processing device having an FM demodulator at low cost and with little performance degradation by obtaining a more accurate quantized output.

[0009]

SUMMARY OF THE INVENTION In order to solve the above-mentioned conventional problems and to achieve the above object, the present invention provides an analog reproduction F / F in a video signal processing for processing an FM signal.
A low-cost A / D converter having a relatively small output bit width is used as an A / D converter for quantizing the M luminance signal.
/ D converter output is input, data is interpolated from several points before and after the input data, and an interpolation filter having a quantized output with higher precision and a wider bit width than the input data is tan.
A video signal processing apparatus that can obtain an FM demodulated output with a relatively small noise component even if a small number of bits are used by providing a signal at a stage preceding the FM demodulator is provided.

More specifically, an interpolation filter provided on the output side of the A / D converter is a high-pass filter that limits the band of the low-frequency side of the output of the A / D converter and removes the DC component. (Hereinafter referred to as HPF) to remove the DC component of the A / D converter by reproducing the data, and to realize the filter by outputting a digital data with higher precision than the input.

The interpolation filter provided on the output side of the A / D converter is reproduced by a low-pass filter (hereinafter referred to as LPF) for band-limiting the high-frequency side of the A / D converter output. Therefore, it can be realized by removing unnecessary components outside the high-frequency FM band and configuring the filter to output digital data with higher accuracy than the input.

Further, an interpolation filter provided on the output side of the A / D converter is replaced with a band-pass filter (hereinafter referred to as BPF) for band-limiting the low and high frequencies of the output of the A / D converter.
, The DC component of the A / D converter and unnecessary components outside the high-frequency FM band are removed, and the filter is configured to output digital data with higher precision than the input.

The digital FM demodulator configured to connect the interpolation filter to the output of the A / D converter allows the A / D converter having an output having a smaller bit width than the input bit width of the digital FM demodulator to be used. A video signal processing apparatus having a configuration for demodulating a digital FM signal of the A / D converter.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of a video signal processing device according to the present invention, FIG. 2 is a diagram showing frequency characteristics of an interpolation filter, and FIG. 3 is an example of a block diagram of an interpolation filter. In the block diagram shown in FIG. 1, the analog reproduction FM luminance signal separated from the video signal is quantized by the A / D converter 11 into, for example, 8 bits. The quantized reproduced FM luminance signal is input to the interpolation filter 12. As shown in FIG. 2, the frequency characteristic of the interpolation filter 12 is constant in the FM band and attenuated in the band above the white clip, so that unnecessary noise components can be reduced. .

The output of the interpolation filter 12 is connected to an FM equalizer 13 so that when the reproduced FM luminance signal decreases due to demagnetization or spacing loss of the magnetic tape, the carrier component and the upper band component are different from the lower band component. To correct the reversal phenomenon that occurs due to the decrease. The FM equalizer here is A
The signal processing may be performed in analog by moving to the input side of the / D converter.

The reproduced FM luminance signal corrected for the inversion phenomenon is a signal (cos) having a constant phase difference of 90 degrees as shown in FIG. 4B with respect to the input signal as shown in FIG. 4A.
Signal) is input to a 90-degree phase delay filter that generates the signal. As a result of dividing the FM reproduced luminance signal, which was the reference in the 90-degree phase delay filter 14, by the cos signal by the divider 15, as shown in FIG. 5, the reproduced FM luminance signal and the cos component of each sample point were obtained. Play FM from Relationship
A tan component for the luminance signal is obtained.

Since the tan component here is a 90-degree phase delay component generated from the reproduced FM luminance signal, that is, a cos component corresponding to the level of the reproduced FM luminance signal, a tan component independent of the input level is obtained. .

The reconstructed FM luminance signal converted into the tan component by the divider 15 is obtained by calculating the inverse function from the tan component by the operation unit 16 to obtain the instantaneous phase component as shown by θ1, θ2, θ3 in FIG. And an angular frequency is obtained by differentiating the instantaneous phase component. The extracted angular frequency is set in a deviation according to various modes of each VTR, and is demodulated as a reproduced video signal.

The above-described FM demodulator generates a DC component for each frequency from a change in the phase component of the input FM waveform. As a result, in order to obtain an FM demodulated output with the noise component reduced as much as possible, data obtained by further dividing the FM demodulator input is required. An example will be described with reference to FIG. For example, when the input signal is 10-bit data c
Then, au and ad become 8-bit data. When this input signal is considered as a cos component, the generated phase component is as shown in FIG. As a matter of course, an 8-bit cos component cannot obtain the accuracy of the 10-bit C point.

Therefore, the phase component obtained from the input is θ
₁ through? No theta ₃ precision in the range of _2, the demodulated output which is calculated from the angular frequency is missing data, it produces a noise component. The foregoing also occurs for the reproduced FM luminance signal, ie, the sin component. Therefore, normally, the output of the A / D converter is set to 9 bits or more.

However, since the signal processing in the FM band is performed, the system clock of the circuit becomes 28.6 Mhz, which is higher than usual, and increasing the number of output bits of the A / D converter requires a rapid cost even in the case of integration. It leads to up.

Therefore, an interpolation filter 12 is inserted between the A / D converter 11 and the FM equalizer 13. FIG. 3 is an example of a block diagram of the interpolation filter, which includes eight-bit latches 31 to 36 connected in cascade and four adders 37.
３１０310 and four coefficient units 311 to 314 are IIR (Finit Inpuse Response) type filters.
Outputs after the decimal point are calculated from the input signals at six adjacent timings multiplied by a factor of 0.5, 0.875, etc. by the coefficient units 311 to 314, for example.

The 8-bit input is interpolated as 10-bit data by giving the demodulator 14 an input signal while maintaining the accuracy of 8 bits + decimal point (for example, 10 bits when 2 bits are valid). Results. With this configuration, 10-bit interpolation data can be obtained as an input signal of the demodulator 14 while maintaining the output of the A / D converter 11 at 8 bits.
The noise component at the time of demodulation can be reduced and, at the same time, the band of the unnecessary component can be limited based on the frequency characteristics of FIG.

Next, FIG. 8 shows an example of an embodiment in which the characteristic of the interpolation filter 12 is a high-pass filter (hereinafter referred to as HPF). The same parts as those of the embodiment shown in FIG.

FIG. 9 shows an example of a frequency characteristic of the HPF 81, and FIG. 10 shows an example of a block diagram of the HPF 81. For example, an 8-bit input signal includes a latch 101 and an adder 103.
, And the other end receives the output of the adder 102. The output of the adder 103 is the coefficient units 104 and 105
The output multiplied by, for example, 0.5 by the coefficient unit 104 is fed back to the other input of the adder 102. Further, the output of the HPF 81 is, for example, an output multiplied by 0.5 by the coefficient unit 105 to form an IIR filter.

In this configuration, since the data below the decimal point is interpolated by the coefficient units 104 and 105 from the data one clock before and the data fed back, the input to the demodulator 14 must have an accuracy of 8 bits or more. become.

Further, as shown in the frequency characteristic shown in FIG. 9, the frequency characteristic has a characteristic capable of removing the DC component of the reproduced FM luminance signal. The configuration of the tan demodulator includes a reproduction FM
After obtaining the absolute value of the output of the cos component of the luminance signal and the reproduction FM luminance signal, the circuit scale is reduced by dividing. Here, when a reproduced FM luminance signal having a DC offset is output due to a quantization error and accuracy variation of the A / D converter 11, an offset always occurs at the time of detecting an absolute value, and as a result, demodulation accuracy is deteriorated. The problem of the DC offset by the A / D converter 11 described above can be absorbed by the HPF 81.

Next, FIG. 11 shows an example of an embodiment in which the HPF 81 and the interpolation filter 12 are connected in cascade and used as a band-pass filter. The same parts as those of the embodiment shown in FIGS. 1 and 8 are denoted by the same reference numerals, and description thereof will be omitted.

Also in this configuration, the decimal point data is interpolated by the HPF 81 and the interpolation filter 12, so that the input to the demodulator 14 has an accuracy of 8 bits or more. Further, since the frequency characteristic has characteristics of both the HPF 81 and the interpolation filter 12, it is possible to remove unnecessary components in a high frequency range without being affected by an input DC offset.

Next, FIG. 12 shows an example of an embodiment in which the interpolation filter 12 is removed from the embodiment of FIG. 1 and 8
The same parts as those of the embodiment shown in FIG.

In this configuration, the output of the A / D converter 11 is directly input to the FM equalizer. Since the FM equalizer is configured to perform data interpolation with decimals less than that performed by the HPF 81 and the interpolation filter 12, the demodulator 14
Input has a precision of 8 bits or more, so that it is possible to perform demodulation without deteriorating the precision.

Next, an embodiment in which the coefficient unit of the HPF 81 in FIG. 8 can be changed will be described with reference to FIG. FIG. 14 is a block diagram showing an example of an interpolation filter for an FM demodulator. FIG. 15 is an example of the frequency characteristic of the filter in FIG. 14, and the same parts as those in FIG. A coefficient unit 131 for, for example, multiplying the input signal by 1.5 is newly provided in the coefficient unit 103 of FIG. 4, and by switching with a switch 132, the DC component is removed as shown in FIG. Limited frequency characteristics can be obtained with a slight increase in the number of gates.

Regarding this filter output, the output maintained at the precision below the decimal point calculated by the coefficient unit is input to the FM demodulator, so that the accuracy does not deteriorate.

[0034]

As described above, according to the present invention, a relatively inexpensive A / D converter with a small bit width is used, and a signal before and after the reproduced FM luminance signal quantized by the A / D converter is used. By providing an interpolation filter for interpolating the output below the decimal point from the data, it is possible to realize an FM demodulator having a characteristic capable of suppressing unnecessary band components without deteriorating the demodulation accuracy. There is an advantage that a system price of a device using a device such as a VTR can be kept low.

Further, according to the present invention, an A / D converter which can be integrated at a low cost is used, and an output below a decimal point is interpolated from data before and after the reproduced FM luminance signal quantized by the A / D converter. A video signal processing apparatus having an FM demodulator having characteristics capable of preventing deterioration of demodulation accuracy due to DC offset of an A / D converter without causing deterioration of demodulation accuracy by providing an HPF. Is obtained.

Further, by connecting the HPF and the interpolation filter in cascade, a video signal processing device having an FM demodulator having both characteristics can be obtained.

Also, by switching the coefficients of the IIR HPF, a video signal processing apparatus having an FM demodulator capable of removing unnecessary high-frequency components of the reproduced FM luminance signal without increasing the number of gates can be obtained. .

Therefore, by using an inexpensive A / D converter with a relatively small number of bits that can be built in and interpolating the output using an interpolation filter to obtain a more accurate quantized output, the cost can be reduced. A video signal processing device having an FM demodulator with little performance degradation can be obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram of a video signal processing apparatus according to an embodiment of the present invention.

FIG. 2 is a characteristic diagram showing frequency characteristics of an interpolation filter according to the present invention.

FIG. 3 is a block diagram of an interpolation filter according to one embodiment of the present invention.

FIG. 4 is a characteristic diagram showing an example of a reproduced FM luminance signal input to the video signal processing device according to one embodiment of the present invention.

FIG. 5 is a characteristic diagram showing an example of a phase component extracted by the video signal processing device according to one embodiment of the present invention.

FIG. 6 is a characteristic diagram showing an example of a reproduced FM luminance signal input to the video signal processing device according to one embodiment of the present invention.

FIG. 7 is a characteristic diagram showing an example of a phase component extracted by the video signal processing device according to one embodiment of the present invention.

FIG. 8 is a block diagram of a video signal processing apparatus according to an embodiment of the present invention.

FIG. 9 is a characteristic diagram showing frequency characteristics of the HPF according to the present invention.

FIG. 10 is a block diagram of an HPF according to an embodiment of the present invention.

FIG. 11 is a block diagram of a video signal processing apparatus according to an embodiment of the present invention.

FIG. 12 is a block diagram of a video signal processing apparatus according to an embodiment of the present invention.

FIG. 13 is a block diagram of an HPF according to an embodiment of the present invention.

FIG. 14 is a view showing frequency characteristics of the HPF according to one embodiment of the present invention.

[Explanation of symbols]

11: analog-digital converter, 12: interpolation filter, 13, 121: FM equalizer, 14: 9
0 degree phase delay filter, 15 ... divider,
16 arithmetic unit, 17 FM demodulator, 31, 3
2, 33, 34, 35, 36, 103 ... latch, 37,
38, 39, 310, 101, 102 ... adder, 31
1,312,313,314,104,105,131
... coefficient unit, 81 ... high-pass filter, 13
2. Switch.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hideo Shidani 1410 Inada, Hitachinaka-shi, Ibaraki Pref. Hitachi, Ltd. Visual Information Media Division

Claims (7)

[Claims] 1. A tan-type FM that digitally encodes an input frequency-modulated (hereinafter referred to as FM) signal and performs FM demodulation on the digital FM signal with a signal that always has a phase difference of 90 degrees.
A video signal comprising a demodulator, and a bit precision extending means for improving data precision in order to reduce a noise level at the time of demodulation and increasing a bit width at an input portion of the FM demodulator. Processing equipment. 2. A helical scan video tape recorder (hereinafter referred to as VTR) for mounting and reproducing at least two or more magnetic heads on a rotating drum to record and reproduce a luminance signal subjected to FM modulation and a color signal subjected to low-frequency conversion. There, FM of reproduction
A video signal processing device comprising a demodulator constituted by a digital circuit, and an input section of the digital FM demodulator having a bit precision extending means for increasing an output bit width for reducing a noise level at the time of demodulation. 3. The bit precision extending means comprises an interpolation filter which produces interpolation data from digital FM signals of several points adjacent to the input data and which has an output whose bit width is larger than that of the input FM signal. 3. The video signal processing device according to claim 1, wherein: 4. The interpolation filter according to claim 1, wherein
4. The video signal processing apparatus according to claim 1, wherein said video signal processing apparatus is constituted by a low-pass filter having characteristics in which a high frequency unnecessary component of the M signal is removed and a band is limited. 5. The digital filter according to claim 1, wherein the interpolation filter is
4. The video signal processing apparatus according to claim 1, wherein the video signal processing apparatus is constituted by a high-pass filter having a characteristic in which a DC component and a low-frequency unnecessary component of the M signal are removed and a band is limited. 6. The interpolation filter according to claim 1, wherein
4. The video signal processing apparatus according to claim 1, wherein the video signal processing apparatus is constituted by a band-pass filter having a characteristic in which a DC component, a low-frequency unnecessary component, and a high-frequency unnecessary component of the M signal are removed and a band is limited. 7. An analog-to-digital converter (hereinafter, referred to as an A / D converter) having an output having a smaller bit width than an input bit width of a digital FM demodulator. 4. The video signal processing apparatus according to claim 1, wherein said video signal processing apparatus demodulates a digital FM signal.